Radio beacons with directional antennas, so-called directional beacons, are used to enable on the one hand a high power to be emitted and on the other hand the position of an OBU (onboard unit) to be located on the coverage range of the directional antenna. However, the use of a directional antenna leads to the problem that other transceivers active on the same channel are difficult to hear or cannot be heard at all outside the radio field of the directional antenna, and this can lead to a disturbance in the radio communication between the beacon and the OBU that is known as a “hidden node” problem.
Various methods for solving the hidden node problem are known such as CSMA/CA (carrier sense multiple access/collision avoidance) with the listen before talk (LBT) principle, as well as the RTS/CTS extension thereof with the exchange of a channel reservation message (request to send, RTS) and a reservation acknowledgement message (clear to send, CTS).